Not hard to imagine how the same forces could cause damage
to a concrete bridge with it's foundation in the water and constantly being
subjected to nearby high speed boat traffic.


High speed is a relative thing. The speed limit in all the channels around here
is 25.

The reality is his bridge is mostly damaged by the 200-400 heavy trucks a day
that cross it daily. (mostly dump trucks and concrete mixers)
The insanity, a speeding ticket for a 40 ton truck going over the bridge is
$80-100 but a 12' jon boat going under the bridge can get a $27,500 fine.
Ain't government great?